Optical switching element having movable optically transmissive microstructure

ABSTRACT

An optical switching element has a movable optically transmissive microstructure to change the optical paths of the optical signals. The movable microstructure is “optically transmissive” because it includes structures such as waveguides and waveguide networks which transmit optical signals. The apparatus uses MEMS and micromachining technology to build an optical switch having an optically transmissive microstructure which moves from one position to another position in a direction (e.g., laterally, vertically, rotationally) such that incoming optical signals align over a small air gap with different waveguides, or with different inputs to the waveguides, depending on the position of the movable microstructure. As a result, the optical signals travel different optical paths (e.g., straight pass through or cross over) depending on the position of the movable microstructure.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application is related to, and claims priority to,provisional U.S. Patent Application Serial No. 60/233,672 by Ying WenHsu, filed on Sep. 19, 2000 and titled “Method for switching opticalsignals using microstructures.”

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This field of the invention relates generally to a class ofdevices and integration of an array of these devices into a system forswitching optical signals. In particular, the devices are made withmaterials and processes that are compatible with the prevalentsemiconductor manufacturing practice, hence capable of producingproducts in high volume and low cost.

[0004] 2. Background

[0005] The interest in these devices has been driven by the tremendousincrease in demand for more usage and faster communications systems,i.e. greater bandwidth, in the telecommunication industry. The primeexamples of applications that are pushing this demand are the Internet,video/music on demand, and corporate data storage. The existingtelecommunication infrastructure, which was largely developed fortelephone calls, is now incapable of meeting the demands for newapplications of data communication.

[0006] Several options have been developed to meet this new demand.These options include wireless, optical, and free-space lasercommunication technologies. To date, the most promising technologycapable of meeting the projected bandwidth requirements of the future isthe optical technology.

[0007] In an all optical network, or in a combination of an optical andelectrical network, the necessary components include a signal carriermedium (i.e. optical fiber), signal routing systems, and data controlsystems. These signal routing systems have devices which switch opticalsignals between optical fibers.

[0008] In the prior art approaches, the switching of optical signals canbe accomplished in predominantly two major approaches: electrical andoptical. Today, most systems use electrical switching. In these systems,at the network junctions, the optical signals must first be convertedinto electrical signals. The converted electrical signals are thenswitched to the designated channel by integrated circuits. Lastly, theelectrical signals must be converted back into optical signals beforethe signals can be passed onto the optical fiber toward the nextdestination. Such optical converters are relatively expensive comparedto the rest of the transmission equipment.

[0009] Electrical switching technology is reliable, inexpensive (exceptfor optical converters), and permits signal reconditioning andmonitoring. The main drawback with electrical switching systems is thatthe number of junctions in a long distance network can be large, and thetotal cost of converters is very high. Furthermore, typically more than70% of signals arriving at a junction require only simple straightpass-through, and conversion (down and up conversions) of the fullsignal results in inefficient use of hardware. System designers alsoanticipate that future systems are best served by transparent opticalswitch capabilities; that is, switching systems capable of redirectingthe path of the optical signal without regard to the bit rate, dataformat, or wavelength of the optical signal between the input and outputports. Most electrical switching systems are designed for a specificrate and format, and cannot accommodate multiple and dynamic rates andformats. Future systems will also be required to handle optical signalsof different wavelengths, which in an electrical switching network wouldnecessitate the use of separate channels for each wavelength. Theselimitations of the electrical switching system provide new opportunitiesfor the development of improved optical switching systems.

[0010] A switch that directly affects the direction of light path isoften referred to as an Optical Cross Connect (OXC). Conventionaloptical fabrication techniques using glass and other optical substratescannot generate products that meet the performance and cost requirementsfor data communication applications. Unlike the electrical switchingtechnique that is based on matured integrated circuit technology,optical switching (ones that can achieve high port count) depends ontechnologies that are relatively new. The use of micromachining is onesuch new approach. The term MEMS (Micro Electro-Mechanical Systems) isused to describe devices made using wafer fabrication process bymicromachining (mostly on silicon wafers). The batch processingcapabilities of MEMS enable the production of these devices at low costand in large volume.

[0011] MEMS-based optical switches can be largely grouped into threecategories: 1) silicon mirrors, 2) fluid switches, and 3)thermal-optical switches. Both fluid and thermal-optical switches havebeen demonstrated, but these technologies lack the ability to scale upto a high number of channels or port counts. A high port count isimportant to switch a large number of fibers efficiently at thejunctions. Thus far, the use of silicon mirrors in a three dimensional(3D) space is the only approach where a high port count (e.g., greaterthan 1000) is achievable.

[0012] Optical Cross Connects that use 3D silicon mirrors face extremechallenges. These systems require very tight angular control of the beampath and a large free space distance between reflective mirrors in orderto create a device with high port counts. The precise angular controlsrequired are typically not achievable without an active control of beampaths. Since each path has to be monitored and steered, the resultingsystem can be complex and costly. These systems also require substantialsoftware and electrical (processing) power to monitor and control theposition of each mirror. Since the mirror can be moved in two directionsthrough an infinite number of possible positions (i.e., analog motion),the resulting feedback acquisition and control system can be verycomplex, particularly for a switch having large port counts. Forexample, as described in a recent development report, LucentTechnology's relatively small 3D mirror-switching prototype wasaccompanied by support equipment that occupied three full-size cabinetsof control electronics.

[0013] Ideally, an optical switch will have the following principalcharacteristics:

[0014] 1) Be scalable to accommodate large port counts (>1000 ports);

[0015] 2) Be reliable;

[0016] 3) Be built at a low cost;

[0017] 4) Have a low switching time;

[0018] 5) Have a low insertion loss/cross talk.

[0019] While the 3D-silicon mirror can meet the scalability requirement,it cannot achieve the rest of the objectives. Therefore, there is a needfor a new approach whereby the complex nature of the 3D free spaceoptical paths and analog control can be replaced with guided opticalpaths and digital (two states) switching. Such a system will greatlysimplify the operation of switching, enhance reliability andperformance, while significantly lowering cost. The disclosure in thefollowing sections describes such a system.

SUMMARY OF THE INVENTION

[0020] The invention relates to a method and apparatus for switchingoptical signals using a movable optically transmissive microstructure.This apparatus uses movable microstructures to direct multiple opticalpaths.

[0021] A first, separate aspect of the invention is an apparatus forswitching optical signals by selectively moving a movable opticallytransmissive microstructure, where the optical signals take one set ofpaths if the microstructure is not moved and the optical signals take adifferent set of paths if the microstructure is moved.

[0022] A second, separate aspect of the invention is an apparatus forswitching optical signals by selectively moving a movable opticallytransmissive microstructure, where the optical path that the opticalsignals take depends on the position of the microstructure.

[0023] A third, separate aspect of the invention is an apparatus forswitching optical signals comprising a fixed input waveguide, at leasttwo optically transmissive waveguides mounted to a movablemicrostructure, and a fixed output waveguide.

[0024] A fourth, separate aspect of the invention is an apparatus forswitching optical signals comprising a movable optically transmissivemicrostructure having an input and an output, where the input ispositioned in close proximity (e.g., a small air gap) to a waveguidecontaining an incoming optical signal and the output is positioned inclose proximity (e.g., a small air gap) to a waveguide for carrying anoutgoing optical signal.

[0025] A fifth, separate aspect of the invention is an apparatus forswitching optical signals comprising a micro structure mounted formovement relative to the substrate of a silicon chip, the microstructurecarrying optically transmissive waveguides.

[0026] A sixth, separate aspect of the invention is an apparatus forswitching optical signals comprising a substrate of a chip, a microstructure carrying optically transmissive waveguides and movably mountedto the substrate for movement relative to the substrate, and a controlstructure for moving the microstructure relative to the substrate.

[0027] A seventh, separate aspect of the invention is an apparatus forswitching optical signals comprising a substrate of a chip, a supportstructure mounted to the substrate, a microstructure carrying opticallytransmissive waveguides and movably mounted to the support structure formovement relative to the substrate, and a control structure for movingthe microstructure relative to the substrate.

[0028] An eighth, separate aspect of the invention is an apparatus forswitching optical signals comprising an optical switch having a movableoptically transmissive microstructure that switches optical signals inthe X-Y dimension and an optical switch having a movable opticallytransmissive microstructure that switches optical signals in the Zdimension, thereby providing the capability to switch optical signals in3 dimensions.

[0029] A ninth, separate aspect of the invention is an apparatus forswitching optical signals comprising a micro-switch element having amovable optically transmissive microstructure, the micro-switch elementbeing capable of directing optical signals from two inputs to any of twooutputs.

[0030] A tenth, separate aspect of the invention is an apparatus forswitching optical signals comprising a movable optically transmissivemicrostructure which corrects optical misalignment from a twodimensional array of optical outputs by using a two dimensional array ofoptic elements placed at the interface.

[0031] An eleventh, separate aspect of the invention is a method ofswitching optical signals comprising the step of selectively moving amovable optically transmissive microstructure, where the optical signalstake one set of paths if the microstructure is not moved and the opticalsignals take a different set of paths if the microstructure is moved.

[0032] A twelfth, separate aspect of the invention is a method ofswitching optical signals comprising the steps of providing an incomingoptical signal through a fixed input waveguide, selectively directingthe optical signal into one of at least two waveguides mounted to amovable microstructure by selectively moving the microstructure, andoutputting the optical signal through a fixed output waveguide.

[0033] A thirteenth, separate aspect of the invention is a method ofswitching optical signals comprising the step of positioning a movableoptically transmissive microstructure having an input and an output suchthat the input is positioned in close proximity (e.g., a small air gap)to a waveguide containing an incoming optical signal and the output ispositioned in close proximity (e.g., a small air gap) to a waveguide forcarrying an outgoing optical signal.

[0034] A fourteenth, separate aspect of the invention is a method ofswitching optical signals comprising the step of mounting an opticallytransmissive microstructure for movement relative to the substrate of asilicon chip, the microstructure carrying optically transmissivewaveguides.

[0035] A fifteenth, separate aspect of the invention is a method ofswitching optical signals comprising the steps of providing a substrateof a chip, movably mounting a microstructure carrying opticallytransmissive waveguides to the substrate for movement relative to thesubstrate, and selectively moving the microstructure relative to thesubstrate to switch the optical signals.

[0036] A sixteenth, separate aspect of the invention is a method ofswitching optical signals comprising the steps of providing a supportstructure mounted to the substrate of a chip, movably mounting amicrostructure carrying optically transmissive waveguides to the supportstructure for movement relative to the substrate, and selectively movingthe microstructure relative to the substrate to switch the opticalsignals.

[0037] A seventeenth, separate aspect of the invention is a method ofswitching optical signals comprising the steps of providing an opticalswitch that switches optical signals in the X-Y dimension and providingan optical switch that switches optical signals in the Z dimension,thereby providing the capability to switch optical signals in 3dimensions.

[0038] An eighteenth, separate aspect of the invention is a method ofswitching optical signals comprising the steps of providing amicro-switch element having a movable optically transmissivemicrostructure capable of directing optical signals from two inputs toany of two outputs.

[0039] A nineteenth, separate aspect of the invention is a method ofswitching optical signals comprising the steps of selectively moving anoptically transmissive microstructure to switch optical signals andcorrecting optical misalignment from a two dimensional array of opticaloutputs by using a two dimensional array of optic elements placed at theinterface.

[0040] A twentieth, separate aspect of the invention is a method offabricating movable and stationary waveguides using a movable opticallytransmissive microstructure.

[0041] A twenty-first, separate aspect of the invention is a method offabricating movable and stationary waveguides using a movable opticallytransmissive microstructure, the method comprising the steps ofintegrating simple switch elements and forming a structure capable ofsimultaneously switching a high density of optical signals from a twodimensional input array to a two dimensional output array.

[0042] A twenty-second, separate aspect of the invention is any of theabove separate aspects, either individually or in some combination.

[0043] Further separate aspects of the invention can also be found in asystem or method that practices any of the above separate aspects,either individually or in some combination.

[0044] Other systems, methods, features and advantages of the inventionwill be or will become apparent to one with skill in the art uponexamination of the following figures and detailed description. It isintended that all such additional systems, methods, features andadvantages be included within this description, be within the scope ofthe invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE FIGURES

[0045] The components in the figures are not necessarily to scale,emphasis instead being placed upon illustrating the principles of theinvention. Moreover, in the figures, like reference numerals designatecorresponding parts throughout the different views.

[0046]FIG. 1 illustrates a block diagram of an example embodiment of anoptical switch system adapted to handle 1024 ports.

[0047]FIG. 2 illustrates an exploded conceptual view of an exampleembodiment of the OXC blocks and optical connectors of FIG. 1.

[0048]FIG. 3A illustrates a plan view of an example embodiment of asingle switching layer of FIG. 2.

[0049]FIG. 3B illustrates an edge view of an example embodiment of asingle switching layer of FIG. 2.

[0050] FIGS. 4A-4F illustrate different example embodiments of awaveguide on a switching layer.

[0051]FIG. 5A illustrates an plan view of an example embodiment of aswitching layer which can switch 8×8 ports.

[0052]FIG. 5B illustrates an edge view of the switching layer of FIG.5A.

[0053]FIG. 6A illustrates an example embodiment of an optical connectorwhose optical substrate is machined to have an array of convex sphericalsurfaces.

[0054]FIG. 6B illustrates how the optical connector of FIG. 6A correctsa misaligned light beam.

[0055]FIG. 7A illustrates an example embodiment of a switch elementhaving a movable optically transmissive platform.

[0056]FIG. 7B illustrates the switch element of FIG. 7A when the movableplatform is not moved.

[0057]FIG. 7C illustrates the switch element of FIG. 7A when the movableplatform is moved.

[0058]FIG. 7D illustrates an example embodiment of a switch elementhaving a movable optically transmissive platform and a double layer ofwaveguides.

[0059]FIG. 8A illustrates an example alternative embodiment of a switchelement having a movable optically transmissive platform which movesparallel to the plane of the substrate.

[0060]FIG. 8B illustrates an example alternative embodiment of a switchelement having a rotatable or pivoting optically transmissive platform.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0061]FIG. 1 illustrates a block diagram of an example embodiment of anoptical switch system 10 adapted to handle 1024 ports by 1024 ports.This optical switch system 10 includes a 3-dimensional waveguide. Theoptical switch system 10 shown in FIG. 1 employs guided wave paths(i.e., waveguide), digital switching, and is capable of handling 1024ports. Two of the key components of the optical switch system 10 are twoOXC blocks 12, 14. OXC blocks 12, 14 are also referred to as switchblocks because they include vertical and horizontal optical switchesrespectively. OXC block (Y) 12 is used for switching optical beams inthe vertical direction, and OXC block (X) 14 switches optical beams inthe horizontal direction. The two OXC blocks (Y and X) 12, 14 areconnected end-to-end such that all outputs of the first (Y) OXC block 12is connected to the input of the second (X) OXC block 14.

[0062] Since each OXC block 12, 14 is an assembled unit, somemanufacturing tolerances may be inevitable. To handle the accumulationof these tolerances, an optical connector 16 is required to facilitatesystem assembly. Likewise, optical connectors 16 may be used at theinput of the first OXC block 12, and output of the second OXC block 14,to allow for positional errors at the interface connection. Optionally,the optical connector 16 can be an optical-to-electrical-to-opticalconnector, a plurality of mirrors in free space, a bundle of opticalfibers, or any kind of optical connector.

[0063] Optical fibers 18 are connected to the input interface 20. Theswitched optical signals exit at the output interface 22. For example,the input interface 20 and output interface 22 may be mechanicalinterfaces to fiber optics. Electrical signals for controllingindividual switch elements are interconnected (between layers) in anelectrical interconnect 24 on the side of each OXC block 12, 14. Theseelectrical wires are routed to the Interface and Control Electronics 30located adjacent to the OXC blocks 12, 14. The optical switch system 10may be mounted on a board 32.

[0064]FIG. 2 illustrates an exploded conceptual view of an exampleembodiment of the OXC blocks 12, 14 and optical connectors 16A-16C ofFIG. 1. For clarity, the vertical switch block, OXC block 12, is shownwith only the first and last switching layers 40, 42. Each switchinglayer 40, 42, for example, is capable of switching 32 inputs to any ofthe 32 outputs in the vertical direction. By placing 32 of the switchinglayers together, all 32 channels can be connected along the verticalplane. To complete the full capability of switching 32×32 channels, amechanism for switching in the horizontal direction is needed and thisis fulfilled, for example, by a second OXC block 14 (the horizontalswitch block). FIG. 2 shows only the first and last switching layers 44,46 of the second (X) OXC block 14. Each switching layer 44, 46, forexample, is capable of switching 32 inputs to any of the 32 outputs inthe horizontal direction. By placing 32 of the switching layerstogether, all 32 channels can be connected along the horizontal plane.Combined into the embodiment shown in FIG. 2, the vertical andhorizontal switching layers create a 32×32 optical switch.

[0065] The following example illustrates how a signal at channel (1,1)(the numbers refer to the row and column number respectively) can berouted to the channel (32,32) output. The optical beam 50 (representedin arrows) enters at the (1,1) location, through first optical connector16A, and enters the first switching layer 40. The switches in the firstswitching layer 40 connect the optical beam from (1,1) to the (1,32)output. The optical signal exits the vertical (Y) switch layers, andpasses and realigns properly through the second optical connector 16Binto the horizontal (X) switching layer at (1, 32). The optical beam nowis routed from position (1,32) to position (32,32), then realigns andexits through the third optical connector 16C.

[0066] The optical switch system 10 may have an optical path network202. The optical path network 202 includes at least one optical pathalong which the optical signal 50 may travel. For example, the opticalpath network 202 may include a mirror, waveguide, air gap, or otherstructures that provide an optical path. In the example embodiment, theoptical path network 202 is a waveguide network 202. One advantage ofthe 3D waveguide embodied in the optical switch system 10 described isthat in this approach it is possible to achieve a large port countwithout a need to control the beam paths precisely and actively. Sincethe optical beam is captured within the waveguides or waveguide networkson each switching layer, only the end connections are critical. Awaveguide network may include a plurality of waveguides such aswaveguide network 202 shown in FIG. 8A. In fact, a waveguide network maycontain only a single waveguide, if desired. Where an embodiment isdescribed as using a waveguide network, it should be understood that theembodiment could use a waveguide instead, and vice versa. Wherealignment is critical, such as at the interface, an optical connector 16will allow for correction of beam misalignment using conventional andinexpensive optics. The simplicity of the resulting 3D waveguide and theprotective environment (e.g., each switching layer can be sealed)further enhances the reliability and robustness of the system, providingbeam paths which are unaffected by temperature, humidity, aging andhandling.

[0067]FIGS. 3A and 3B illustrate a plan view and an edge viewrespectively of an example embodiment of a single switching layer ofFIG. 2, for example, switching layer 44. This example shows how 32inputs can be connected through an array of simple switch elements 60,to 32 outputs. In this example of a 32×32 port, there are 80 switchelements 60. The methodology of interconnection is well known to thoseskilled in the art of signal routing design and may be any methodology.Pioneering work in routing theories done at Bell Laboratories has shownthat an optical signal can be efficiently routed by connecting simpleswitches (such as 2×2 elements) in a specific manner. By following theserouting guidelines, it can be shown that every input can be connected toany output without any of the connections blocked.

[0068] The switching layer 44 shown in FIGS. 3A, 3B includes a substrate62 that carries waveguides 64 and switch elements 60. In this exampleembodiment, the substrate 62 may be any semiconductor material such assilicon. To protect these waveguide and switch element microstructures,the substrate 62 may be covered and sealed by using another (cap) wafer63. An effective sealing to exclude contaminants and humidity can beachieved by bonding a cap wafer 63 to substrate 62 using any of amultitude of techniques already available, including anodic, fusion, andeutectic bonding.

[0069] Optical signals 50 enter the switching layer 44 at one edge.Preferably, the edge is polished and angled to allow a completerefraction of the optical beams 50. Depending on the optical index ofthe interface medium (e.g., air or another optical element), the angleof the edge can be designed to accommodate total refraction. Once theoptical beam 50 enters the waveguide 64, light cannot escape from thewaveguide 64 due to a phenomenon known as total internal reflection.This is the same phenomenon that allows an optical fiber to carry lightfor long distances without significant loss.

[0070] The switching action is controlled by the application ofelectrical voltage. Each switch element 60 requires, for example, threeelectrical connections: an actuation electrode, a position sensingelectrode, and electrical ground. The electrical ground connection canbe tied together to minimize the number of electrical traces. Eachswitch element 60 would have, therefore, a minimum of two electricalconnections that need to be passed through and underneath the cappingwafer 63 to interface with the outside world. In FIG. 3A, the electricaltraces 66 are shown traversing substantially orthogonally to the opticalpath and terminating at the electrical bond pads 68 at the lower edge.Of course, the actual layout of the electrical traces 66, bond pads 68,input ports and output ports can be modified to be different than thatshown in this example.

[0071] FIGS. 4A-4F illustrates various example embodiments of awaveguide 64 on a switching layer. To maintain total internal reflection(TIR), the environment surrounding the waveguide 64 must have an opticalindex of refraction lower than index of the waveguide 64. Glass, forexample, which has an index of 1.5, can be coated with a material havinga lower index, or simply use a vacuum (index 1.0) or air as the medium.A wide range of gases could be used to ensure compatibility with thewafer bonding process. In a first embodiment, FIG. 4A illustrates across section of a waveguide 64 formed of glass whereby the mediumsurrounding the waveguide 64 is in a vacuum or air. The carrier 70 maybe formed of glass or silicon. In a second embodiment, FIG. 4Billustrates another waveguide 64 where the top and sides of thewaveguide 64 are in contact with a vacuum while the bottom surface isbonded with an intermediate material with an index lower than that ofthe waveguide. The carrier 70 may be formed of glass or silicon.

[0072] In both of the FIG. 4A and 4B embodiments, the upper substrateshould be a material that will transmit optical signals at thewavelength of interest, such as 0.82, 1.3, and 1.55 micrometers. Theseare the wavelengths that are typically used in fiber opticstransmission, and in which the support equipment (such as thetransmitter, carrier and receiver) is designed to handle. In bothembodiments, the material on the bottom (carrier substrate 70) is usedmainly to provide mechanical support to the structure. As it will beexplained later, the actual switching mechanism will require some of thewaveguides to move vertically or laterally by the application of anexternal force. The carrier substrate 70 can be made of glass, silicon,or any material compatible with micromachining.

[0073]FIGS. 4C and 4D illustrate alternative embodiments of a waveguide64 without using a substrate 70. The small amount of material 72 thatbridges the waveguide 64 to adjacent material will allow some loss oflight and this design needs to consider the tradeoff between mechanicalstrength and optical loss. One advantage of the embodiments in FIGS. 4Cand 4D is that only a single-layer structure is required, avoiding thenecessity of wafer bonding. Detailed designs using these alternativeembodiments should involve achieving a balance between the mechanicaland optical integrity of the waveguides and acceptable manufacturingcosts.

[0074] Although the preferred embodiment of an optical switch systemuses a waveguide, optical guides using reflective surfaces or otherknown structures can also be used. FIG. 4E shows a guide 78 made bybonding two wafers 80, 82 to create a closed optical guide 78. Toenhance the reflectivity of the surface, metal coating such as gold ornickel (or any other materials compatible with the micromachiningprocess) could be deposited on the inner surfaces prior to bonding.

[0075] Yet another alternative embodiment is to use the verticalsurfaces of the microstructure. As in a conventional optical system,such an approach would require tight angular control of the verticalwalls to control the beams precisely. FIG. 4F shows a trench etched intothe wafer whose vertical walls are the reflective surfaces with a topcap 80 forming a closed waveguide 78. As before, a metal coating can beapplied to enhance reflectivity.

[0076]FIGS. 5A and 5B illustrate a plan view and an edge view of anexample embodiment of a non-blocking switching layer 44 that performsswitching of 8×8 ports. To achieve full switching capability in thisexample, 12 switch elements 90 are required. Each switching element 90is capable of performing a 2×2 switch. The switching layer 44 isnon-blocking because the optical signal 50 always passes to the opticaloutput side through some optical path.

[0077] Optical connectors 16 are used to minimize insertion loss due tomisalignment between the optical fiber and the switch element 90, orbetween OXC blocks. In both cases, there is an accumulation ofgeometrical tolerances due to imperfect assembly, which should becorrected to minimize loss of light. Most often, the misalignment is dueto a combination of linear and angular offsets.

[0078]FIG. 6A illustrates an optical connector 16 whose substrate ismachined on both sides to have an array of convex spherical surfaces100. One side of the spherical surface array is positioned to connectwith a fiber bundle to receive the incoming light beam 50. The oppositeconvex surface focuses the beam onto a small spot to allow forconnection to the OXC blocks. For example, the optical connector 16 mayhave as a spherical surface 100 for each port in the optical switchingsystem (here, e.g., 32×32, or 1024 surfaces 100).

[0079]FIG. 6B illustrates how the optical connector of FIG. 6A correctsa misaligned beam of light. Let us presume a light beam 50 entering onthe left that will normally be out of the range of the entrance to theOXC block or other optical passage. If uncorrected, the light beam 50will not properly enter the entrance to the OXC block. However, themisaligned beam 50, after being corrected by a spherical surface of theoptical connector 16 will emerge from the optical connector 16 focusedon an image point 102. By placing the entrance pupil of the OXC block oroptical fiber entrance at or near the image point 102, the emerginglight beam will be approximately centered and will enter the opticalpassage such as a waveguide 64 at an incident angle that will becaptured by a total internal reflection process. Other type of surfacesother than spherical can also be used to enhance the quality of theemerged beam. The detailed design of the optical surfaces and selectionof the optical material can include those known to those skilled in theart of optical design.

[0080] The optical connector 16 which uses convex spherical surfaces 100can be manufactured using a series of spherical balls and securing thoseballs in a plate with precisely machined holes. To hold the balls inplace, the simplest method is to shrink the balls in a cold bath (e.g.,liquid nitrogen) and inserting the balls into the holes of the plate.Proper methods of fixture will allow a large number of balls to beinserted simultaneously and precisely. Alternatively, specializedtooling with convex grinding tool bits can be made to produce thedesired surfaces. The possible manufacturing techniques are numerous andinclude those well known to those skilled in the art of opticalmanufacturing.

[0081]FIG. 7A illustrates an example embodiment of a small switchelement 60 made by a micromachining process. This example embodiment isof a 2×2 switch element 60 because there are two inputs and two outputs;of course, the number of inputs and the number of outputs can beincreased or decreased. The embodiment of the switch element 60 has twowaveguides integrated on top of a carrier platform 110. The combinedstructure (waveguide and carrier) is bonded to a substrate 62 andpositioned such that the switch element 60 is suspended over an air gapover, or a cavity 111 previously etched on, the substrate 62. Thecarrier platform 110 is preferably suspended approximately 30 micronsabove the actuation electrodes 112. The waveguides 114, 116 aretypically less than 10 microns and in this example, the small channelsize is necessary to ensure transmission of only single-mode opticalsignals. The size of the structure and the design of the support springs130 depend on the type of actuation mechanism used. The embodiment willuse electrostatic attraction as the means of actuation.

[0082] For electrostatic actuation, both the carrier platform 110 andthe stationary electrodes 112, 126 have to be electrically conductive,thereby causing the carrier 110 to move toward the electrodes 112, 126,as illustrated in FIGS. 7B and 7C. If the carrier platform 110 is madeout of dielectric materials, it can be made conductive by coating thebottom (i.e., the surface facing the stationary actuation electrode 112)with a metal such as gold or nickel. If the carrier platform 110 is madeof semiconductor materials such as silicon, it can be doped to increaseelectrical conductivity. Opposing and parallel to the carrier platform110 are the stationary electrodes 112, 126 patterned on the bottom ofthe cavity 111. These electrodes 112, 126 connect to the top of thesubstrate 62 by traces patterned on the sloped surfaces. In the cavity111, two stationary electrodes 112, 126 are made, one electrode 112 foractuating movement of the carrier platform 110 and the other electrode126 for feedback sensing of the position of the carrier platform 110.

[0083] This example embodiment of the switch element 60 operates asfollows. Optical signals 50 enter on the left of the switch element 60at locations A and B. The optical signals 50 enter the waveguides 114,116 and cross over due to the particular configuration of the waveguidesin this embodiment. The optical signals 50 from locations A and B exitthe switch element 60 at locations D and C respectively. The originaloptical signals 50 have crossed from A to D and from B to C. When nocrossing of the optical signals 50 is desired in this particularembodiment, an electrical signal is required from the control hardware.By applying a voltage to the fixed electrodes 112 on the substrate 62and a different voltage to the electrode of the carrier platform 110,the voltage difference will result in an electrostatic attraction force.Such a force will pull the carrier platform 110 (and the waveguides 114,116 carried by the carrier platform 110) down (here, less than 10micrometers) toward the fixed electrodes 112, 126 by bending the supportsprings 130, and therefore, in the process remove the waveguides 114,116 from the optical path. The optical signals 50 from location A thenpass directly (through free space 120) toward point C, and the opticalsignals 50 from location B pass directly (through free space 122) tolocation D. FIG. 7B illustrates the case where the carrier platform 110is in its rest state because no power is applied to the actuationelectrode 112; here, the optical signals 50 from locations A and B ofthe fixed waveguides at the input side of the carrier platform 110 crossover in movable waveguides 114, 116 to locations D and C, respectively,of the fixed waveguides at the output side of the carrier platform 110;waveguides 114, 116 are considered “movable” because they move with themovement of the carrier platform 110. When power is applied to theactuation electrode 112, FIG. 7C illustrates the resulting configurationwhere the carrier platform 110 has moved toward actuation electrode 112;here, the optical signals 50 from locations A and B of the fixedwaveguides at the input side of the carrier platform 110 pass directlythrough free space to locations C and D, respectively, of the fixedwaveguides at the output side of the carrier platform 110 becausemovable waveguides 114, 116 have moved out of range of the opticalsignals 50.

[0084] Other methods of actuation are also viable. Electrostaticactuation is preferred because of the simplicity in design andoperation. The main drawback is the higher voltage required to operatethe resulting device, due to the large gap, typically ranging from 20 to100 volts. Alternative actuation methods include magnetic and thermaltechniques. These methods are well known to those skilled in the art ofmicromachine design.

[0085] The sensing electrode 126 on the substrate 62 is used to detectthe position of the carrier platform 110 by sensing changes incapacitance between the electrode 126 and the electrode of the carrierplatform 110 due to changes in the gap caused by movement of the carrierplatform 110. Other means of sensing, such as piezo-resistive, magnetic,optical schemes are also viable. The signal from the sensing electrode126 is used (through close-loop control) to accurately position thewaveguides 114, 116 over the optical entrance and exit.

[0086] The primary loss of optical signal will be at the entrance of themovable waveguides 114, 116 (on the carrier platform 110 of the switchelement 60) and at the entrance of the fixed waveguides. Reducing thedistance between the locations A/C and between B/D can minimize suchloss. To fully minimize loss, but with increased manufacturingcomplexity, a secondary waveguide 138, 140 can be designed on the bottomof the carrier platform 110. In that case, the opening between thestationary waveguides and the movable waveguides 114, 116 can be reducedto less than 2 microns, depending on the etching process. FIG. 7Dillustrates a carrier platform 110 with waveguides 114, 116 on top andwaveguides 138, 140 on the bottom, with one set designed for straightpass and the other for crossover. As is apparent from the embodimentshown in FIG. 7D, in the case where the carrier platform 110 is in itsrest state because no power is applied to the actuation electrode 112,the optical signals 50 from locations A and B of the fixed waveguides atthe input side of the carrier platform 110 pass through movablewaveguides 138, 140 to the fixed waveguides at the output side of thecarrier platform 110. Likewise, when power is applied to the actuationelectrode 112, the carrier platform 110 moves toward actuation electrode112 so the optical signals 50 from locations A and B of the fixedwaveguides at the input side of the carrier platform 110 now passthrough waveguides 114, 116 of the fixed waveguides at the output sideof the carrier platform 110 because movable waveguides 138, 140 havemoved out of range of the optical signals 50 and movable waveguides 114,116 have moved into range of the optical signals 50. Of course, in anembodiment which uses double movable waveguides, such as thatillustrated in FIG. 7D, the default can be either straight pass orcrossover. In other words, waveguides 114, 116 can permit a straightpass while waveguides 138, 140 causes a cross over, or vice versa.

[0087] An alternative embodiment of a MEMS optical switch element 60 isnow described. The movement of the switch element 60 is not limited tothose in the vertical direction perpendicular to the substrate 62. FIG.8A illustrates an example alternative embodiment of a MEMS switchelement whereby the actuation direction is lateral or substantiallyparallel to the plane of substrate 62. FIG. 8B illustrates an examplealternative embodiment of a MEMS switch element which relies onrotational movement. Of course, an optical switching system 10 may becreated from optical switch elements which all move in the same manner(e.g., all move vertically, all move laterally, or all moverotationally) or optical switch elements which move in different manners(e.g., some move vertically and others move laterally, or some movevertically and others move rotationally, or some move laterally andothers move rotationally). The lateral movement can be induced byapplying different voltages to the inter-digitated (known as combfingers in MEMS) structures as shown in FIG. 8A. Describing what isillustrated in FIG. 8A, the MEMS switch element 60 comprises a substrate62. Suspended above substrate 62, for example over a cavity orotherwise, is a movable optically transmissive platform 110. Platform110 is stated to be “optically transmissive” because it has structures(e.g., waveguide networks 200, 202) which transmits optical signals orlight beams 50; it is not intended to mean that the entire platformitself must be optically transmissive. One side of the platform 110 iscoupled to support springs 130 and the opposite ends of the supportsprings 130 are coupled or anchored to the substrate 62. The platform110 has electrodes 204. In this example, electrodes 204 areinter-digitated with actuation electrodes 112. By applying differentvoltages to the electrodes 204 and actuation electrodes 112 on one sideof the platform 110 as compared to the other side of the platform 110,the platform 110 moves in a lateral, or substantially parallel, mannerrelative to the plane of the substrate 62. In FIG. 8A, this lateralmovement means that the platform 110 moves up or down.

[0088] The platform 110 carries waveguide networks 200, 202 where theoptical paths from the input side of optical signals 50 to the outputside change depending on the lateral position of the platform 110. Forexample, if the platform is in a first position (e.g., a rest position),the alignment of the incoming optical signals 50 to the inputs A, B, Cand D of the waveguide networks 200, 202 is selected such that opticalsignals 50 enter inputs C and D. Because of the particular configurationof this example of the waveguide networks 200, 202, optical signals 50which enter inputs C and D of the waveguide networks 200, 202 cross overand exit at outputs H and F respectively. If the platform 110 is thenmoved to its second position, incoming optical signals 50 would enterinputs A and B, and pass straight through to outputs E and Grespectively. Of course, the waveguide networks 200, 202 can be swappedso that the default is a straight pass through. The waveguide networksmay be configured in any shape or form to accomplish whatever opticalpaths are desired.

[0089] The lateral movement approach as shown in FIG. 8A has theadvantage of not requiring the bottom electrodes, thus reducing severalsteps in the manufacturing process. The disadvantage is that the amountof electrode area is limited due to the short height of the resultingstructure, and as a result, a large number of comb fingers may berequired to generate a sufficient attraction force. A significantlylarger electrode area may be required to operate the laterally-movingswitch element of FIG. 8A than the vertically-moving switch element ofFIG. 7A.

[0090] Turning to FIG. 8B, the movable optically transmissive platform110 moves in a rotational or pivoting fashion relative to the substrate.To accomplish rotational movement in a switch element 60, the sameelectrostatic attraction forces as used in the preferred embodimentswill work. For sensing the position of the platform 110, similarcapacitance detection techniques described in the preferred embodimentswill apply. As illustrated, this example embodiment of a rotatingplatform 110 causes inputs A and B to align with the optical signalswhen the platform 110 is in a first position. When the platform 110rotates to its second position, inputs C and D are now aligned with theoptical signals. As with all of the embodiments, the waveguides andwaveguide networks may be configured in any desired shape to achieve thedesired optical paths.

[0091] While various embodiments of the application have been described,it will be apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible that are within the scopeof the subject invention. For example, each feature of one embodimentcan be mixed and matched with other features shown in other embodiments.Features known to those of ordinary skill in the art of optics maysimilarly be incorporated as desired. Additionally and obviously,features may be added or subtracted as desired and thus, a movableplatform having more than two sets of optical paths is alsocontemplated, whereby the platform moves to any one of three or morepositions such that each position activates a different set of opticalpaths. As another example, the optical switch may accept more than 2inputs and provide more than 2 outputs. The optical switch may becombined so as to create bigger optical switches with more ports.Accordingly, the invention is not to be restricted except in light ofthe attached claims and their equivalents.

What is claimed is:
 1. An apparatus for switching an optical signal froma first optical path to a second optical path, the apparatus comprising:a substrate; a micro-machined platform adapted to move relative to thesubstrate; an actuation mechanism to cause the platform to move from afirst position to a second position relative to the substrate; and awaveguide network having a first input and a second input, the waveguidenetwork coupled to the platform such that the waveguide network moveswith the platform, whereby when the platform is in the first position,the optical signal enters the first input and travels along the firstoptical path in the waveguide network, and when the platform is in thesecond position, the optical signal enters the second input and travelsalong the second optical path in the waveguide network.
 2. The apparatusof claim 1 wherein the platform is adapted to move vertically relativeto the substrate.
 3. The apparatus of claim 1 wherein the platform isadapted to move laterally relative to the substrate.
 4. The apparatus ofclaim 1 wherein the platform is adapted to move rotationally relative tothe substrate.
 5. The apparatus of claim 1 wherein the waveguide networkincludes a plurality of waveguides.
 6. The apparatus of claim 5 whereinthe plurality of waveguides include at least a first and secondwaveguide positioned vertically with respect to each other such thatmovement of the platform selects between the first and second waveguidesdepending on their vertical position relative to the substrate.
 7. Theapparatus of claim 5 wherein the plurality of waveguides include atleast a first and second waveguide positioned laterally with respect toeach other such that movement of the platform selects between the firstand second waveguides depending on their lateral position relative tothe substrate.
 8. The apparatus of claim 5 wherein the plurality ofwaveguides include at least a first and second waveguide positioned atan angular offset with respect to each other such that movement of theplatform selects between the first and second waveguides depending ontheir angular offset.
 9. The apparatus of claim 1 further comprising asupport structure for suspending the platform over the substrate. 10.The apparatus of claim 1 wherein the substrate includes a cavity or airgap over which the platform is suspended.
 11. The apparatus of claim 1further comprising an input stationary waveguide coupled to thesubstrate and positioned to transmit the optical signal to either thefirst input or the second input of the waveguide network.
 12. Theapparatus of claim 1 further comprising an output stationary waveguidecoupled to the substrate and positioned to receive the optical signalfrom the waveguide network.
 13. The apparatus of claim 11 furthercomprising an output stationary waveguide coupled to the substrate andpositioned to receive the optical signal from the waveguide network. 14.The apparatus of claim 1 wherein the waveguide network includes a firstoutput and a second output.
 15. The apparatus of claim 14 furthercomprising an output stationary waveguide coupled to the substrate andpositioned to receive the optical signal from either the first output orthe second output of the waveguide network.
 16. The apparatus of claim 1further comprising an activation electrode coupled to the platform andwherein the actuation mechanism includes an actuation electrodepositioned to interact electrostatically with the activation electrode.17. The apparatus of claim 16 wherein the actuation electrode andactivation electrode are inter-digitized.
 18. The apparatus of claim 1further comprising an optical connector positioned at either the inputto the waveguide network or the output of the waveguide network.
 19. Theapparatus of claim 18 wherein the optical connector includes analignment correction surface that corrects an alignment trajectory errorof the optical signal.
 20. The apparatus of claim 19 wherein thealignment correction surface is a spherical surface.
 21. The apparatusof claim 1 wherein the waveguide network includes a waveguide surroundedby a medium, the medium being in a vacuum or air.
 22. The apparatus ofclaim 1 wherein the waveguide network includes a waveguide having a top,bottom and sides, where the top and sides of the waveguide are incontact with a vacuum or air while the bottom is bonded with anintermediate material with an index of refraction lower than that of thewaveguide.
 23. The apparatus of claim 1 wherein the waveguide networkincludes a waveguide formed in a unitary structure with the substrate.24. The apparatus of claim 1 further comprising a sensing electrode fordetermining the position of the platform.
 25. The apparatus of claim 1wherein if the platform in the first position, the optical signalswitches from the first optical path to the second optical path duringtransmission through the waveguide network and if the platform in thesecond position, the optical signal is passed straight through thewaveguide network.
 26. The apparatus of claim 1 wherein if the platformin the first position, the optical signal is passed straight through thewaveguide network and if the platform in the second position, theoptical signal switches from the first optical path to the secondoptical path during transmission through the waveguide network.
 27. Amethod of switching an optical signal from a first optical path to asecond optical path, the method comprising the steps of: propagating theoptical signal toward a platform adapted to move relative to asubstrate, the platform including a waveguide network having a firstinput and a second input, the waveguide network being coupled to theplatform such that the waveguide network moves with the platform;determining whether the optical signal is to propagate along the firstor second optical path; and selectively moving the platform to a firstposition or a second position relative to the substrate, whereby whenthe platform is in the first position, the optical signal enters thefirst input and travels along the first optical path in the waveguidenetwork, and when the platform is in the second position, the opticalsignal enters the second input and travels along the second optical pathin the waveguide network.
 28. The method of claim 27 further comprisingthe step of correcting an alignment trajectory error in the opticalsignal.
 29. The method of claim 28 wherein the step of correcting analignment trajectory error in the optical signal uses a sphericalsurface to correct the error.
 30. The method of claim 27 wherein thestep of moving the platform moves the platform vertically relative tothe substrate.
 31. The method of claim 27 wherein the step of moving theplatform moves the platform laterally relative to the substrate.
 32. Themethod of claim 27 wherein the step of moving the platform moves theplatform rotationally relative to the substrate.
 33. The method of claim27 wherein the waveguide network includes first and second waveguidespositioned vertically with respect to each other such that movement ofthe platform selects between the first and second waveguides dependingon their vertical position relative to the substrate.
 34. The method ofclaim 27 wherein the waveguide network includes first and secondwaveguides positioned laterally with respect to each other such thatmovement of the platform selects between the first and second waveguidesdepending on their lateral position relative to the substrate.
 35. Themethod of claim 27 wherein the waveguide network includes first andsecond waveguides positioned at an angular offset with respect to eachother such that movement of the platform selects between the first andsecond waveguides depending on their angular offset.
 36. The method ofclaim 27 further comprising the step of sensing the position of theplatform.
 37. The apparatus of claim 1 wherein the substrate is asemiconductor.
 38. The method of claim 27 wherein the substrate is asemiconductor.
 39. The apparatus of claim 1 wherein the substrate isquartz.
 40. The method of claim 27 wherein the substrate is quartz. 41.The apparatus of claim 1 wherein the substrate is silica.
 42. The methodof claim 27 wherein the substrate is silica.
 43. The optical switchingsystem of claim 2 wherein the optical connector comprises anoptical-to-electrical-to-optical connector.
 44. The optical switchingsystem of claim 2 wherein the optical connector comprises an bundle ofoptic fibers.
 45. The optical switching system of claim 2 wherein theoptical connector comprises a plurality of mirrors.